Out of the Pack - Finally, I'm Playing MIDI Notes using MAC/65 Assemble

RSS Bot · May 8, 2019

Do you remember me mentioning that the first attempt to write a machine language program to read MIDI data delivered to the Atari joystick port was a complete failure? The Arduino hardware has remained the same. The joystick trigger and cassette motor control(CMC) pin on the SIO port are still being used to control data flow. But this time I redefined the project specs to simplify the ML program and tested the ML data transfer routine as a USR call.

The USR routine was written to replace the BASIC code that checked the joystick trigger to see if data is ready to be read, gets the data, and tells the Arduino to get the next byte by setting the CMC. (the subroutine starting at line 100 in many of the earlier programs) The data byte is stored in a page Zero location to be PEEKed after control is returned to BASIC.

Once working as a USR call the PLA was removed and the M65 file was edited and saved for later inclusion in the Project file as a subroutine. #INCLUDEd READMIDI.M65 routine is as follows:

READMIDI.M65

 
The Arduino had to be reprogramed to minimize the data being sent to the Atari.  The Arduino will first look for MIDI data for channel one.  If its a NOTEON or NOTEOFF command it reads the following MIDI note number and then the volume byte.  It then makes the decision to send a note number to start or change the pitch OR turn off the note being played.  The logic makes sense considering a NOTEOFF command can be transmitted for a note that isn't being played or a NOTEON can set the volume to ZERO.

 
SINGBYTE.M65

 
A sound recording didn't seem to be necessary and the Arduino interface has been explained in previous blog entries.  The atr file contains the MAC/65 files and BASIC files used to create and test the USR input routine.

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